Chemical properties of modified titania hydrolysates

Titania hydrolysates prepared from unmodified and tetraisopropoxytitanium(IV) modified by replacement of the tetraisopropoxy groups with carboxylic acids were studied by FT-Raman, potentiometric titration and electrokinetic sonic amplitude (ESA) measurements. FT-Raman spectroscopy shows that the νsym(COO) and νantisym(COO) stretching modes are observed at 1413 and 1551 cm−1 in modified alkoxide spectra. The Δν of ±140–170 cm−1 implies a bridging type of carboxylate coordination in the modified alkoxides. The 1576 cm−1 band is found in all modified alkoxide and hydrolysate spectra, except for the acetate-modified hydrolysate. The νsym(COO) stretching mode is not observed in the hydrolysate spectra, indicating that the 1576 cm−1 band is a combination mode of ν(Ti–O) stretch (∼560 cm−1) and ν(C–O)Ti stretch (1022 cm−1). Potentiometric titrations show that five equivalence points are detected in the potentiometric titration curves of modified hydrolysates. Three pKa values of pH ≈ 2.7, 6.1 and 9.4 are common to all hydrolysates. Modified hydrolysates exhibit other equilibria with values of pKa ≈ 4.8 and 7.3. Unmodified hydrolysates have another equilibrium at pKa ≈ 8.2. The lack of measurable IEPs correlates with increasing quantities of residual carboxylate groups and increasing alkyl chain length.